Outdoor black slate

We have a outdoor breezeway with black slate that was installed 7 months ago. It is very dull and has lots of dusty dirt on it. When we rinse with a hose it looks great but then dries to the same dullness and dirty look. Can I use vinegar and water on it and scrub, or what product do you have that would be best for it and keep it looking not so dirty? Thank you.

 

Dear Carol:

It sounds like it was not the right type of slate to be installed outdoors.

Or maybe it was, but then they applied an impregnating sealer or, worse yet, a topical sealer to it…

Whatever…

It appears that you have an efflorescence problem.

Efflorescence is the result of a chemical reaction that goes on with certain stones when there's migration of moisture from the ground through the core of the stone. The resulting mineral salt bleeds onto the surface and gives you the impression that the stone surface is dull and dirty. Of course, when it's wet, everything looks nice again…

This chemical reaction does not happen with all stones; it all depends on their mineralogy and natural degree of densisty. That is why it's important selecting a stone with a good track record if you plan to install it outdoors.

Also, if you get an appropriate stone (for outdoor installations), but then you “suffocate” it with a sealer (because that's the “new religion” out there), even an appropriate stone could turn out into a non appropriate one.

Solution to the problem?

None, alas… :-(

 

Man, does the world need marblecleaning.org or what?!

 

It won't do much good to you now, but may I ask you now to please read and e-sign our Statement of Purpose at: http://www.marblecleaning.org/purpose.htm?   At least you will be helping future fellow consumers. :-)

Ciao and good luck,

Mauri z io Bertoli

 

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